Seat back



FIG. 1 is a perspective view of a seat back of the new design;

FIG. 2 is a front elevational view of the seat back of FIG. 1;

FIG. 3 is a rear elevational view of the seat back of FIG. 1;

FIG. 4 is a left side elevational view of the seat back of FIG. 1, the right side elevational view being a mirror image;

FIG. 5 is a top plan view of the seat back of FIG. 1; and,

FIG. 6 is a rear perspective view of the seat back of FIG. 1.

The portions of the Figures shown in broken lines are not part of the claimed design and are for illustration only. 

The ornamental design for a seat back, as shown and described. 